Circuit interrupter



Dec. 26, 1939. R, m 2,185,039

CIRCUIT INTERRUPT-ER Filed Sept. 18, 1954 .2! WITNESSES: 'INVENTOR Law/z /Fj770%.

k BY I u.

I to cause a rupture of the walls defining the arc Patented Dec. 26, 1939 CIRCUIT INTERRUPTER Lewis R. Smith, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 18, 1934, Serial No. 744,532

29 Claims.

My invention relates to circuit interrupters and particularly to high voltage circuit interrupters of the type wherein an expulsive gas blast is utilized for extinguishing the are which is formed incident to the opening of the controlled circuit.

One of the best known forms of expulsive circuit interrupters is the expulsion fuse. These devices usually comprise a tubular arc passage, a means such as a fuse for establishing an are within the tubular arc passage, and a means for producing and expulsive blast of arc extinguishing gas which flows longitudinally through the arc to effect its extinguishment. The simplest means so far developed in the art for producing this gas blast consists in the provision of a lining for the arc passage which is formed of a material that is capable of evolving considerable quantities of an arc extinguishing gas when placed in proximity to an electric arc. The efiiciency and the reliability of operation of the devices depends to a great extent upon the amount and the chemical characteristics of the gas which is caused to expulsively flow through the arc during the circuit interrupting operation, and one of the principal problems of the art has always been the securing of an adequate volume of gas having a satisfactory chemical composition.

The rate of evolution of gas from the surface of the lining of the arc passage depends to a great extent upon the intimacy of contact between the lining and the arc, and it is obvious that the maximum possible evolution of gas (and the most efficient operation of the interrupter) will be effected when the are completely fills the arc passage. Unfortunately, however, the magnitude of the overload current in most present-day circuits varies through wide limits and the physical dimensions of the are likewise vary in almost a direct proportion. At first glance, it might appear that this would not create any serious difiiculties, since the arc passage could be made small enough to cause an intimate engagement between the lining and the surface of the smallest magnitude are that might be drawn within that passage.

The problem is not so simply solved, however, because while intimate engagement between the lining of the arc passage and the arc is imperative, it is possible to have anarc passage which is too small. If this occurs, and large magnitude arcs are drawn therein, the volume of the gas generated may be sufliciently large passage, and even if the walls of the passage are not ruptured, the surfaces of those walls which are exposed to the arc may be heated sumciently to become conducting and thereby make the interruption of the controlled circuit impossible.

This possibility of actual destruction of the circuit interrupter or failure of the device to operate during the occurrence of very heavy overload conditions makes it necessary that the physical dimensions of the arc passage shall be sufficiently large to permit an arc having the largest possible current magnitude, considering the circuit with which the device is to be used, to be established within the arc passage without danger of rupture or excessive heating. If a cylindrical arc passage is utilized, the obvious result will be that for most circuits the passage must have a very considerable cross-sectional area, and when the interrupter is in use on such circuits, the low magnitude arcs produced by the v normal overloads will but partially fill the arc passage. Under such conditions only a small volume of gas will be generated and the efllciency of theinterrupter will be very low. In fact, if the current magnitude of the arc is very small and the dimensions of the arc passage even reasonably large, a small current are drawn therein may not be extinguished at all.

To overcome this diificulty and to assure efficient operation of the interrupter under varying conditions of arc current, the prior art structures have utilized a number of differing arrangements. One of these consisted in the provision of an expulsion fuse wherein the arc passage takes the substantial form of a hollow cylinder. By properly proportioning the dimensions of this cylinder, it is possible to secure an intimate engagement between the opposing surfaces which define the arc passage over a rather large range of current values. For intermittent operation, this arrangement is very satisfactory and meets practically all operational requirements. It has one disadvantage, however; if a large number of arcs of moderate current value are established within the device and therein interrupted, considerable localized erosion of the walls which define the arc passage may result. The effect of this erosion will be to cause a section of the arc passage to have a considerably greater width than the normal separation of the surfaces which define that passage, then, upon the establishment of lowcurrent arcs within the arc passage, those arcs will probably exist within this enlarged section and may not intimately contact the gas evolving walls of the arc passage.

The result, of course, will be a progressive enlargement of the eroded section which eventually will cause the device to become incapable of opening the controlled circuit.

The principal object of my invention, therefore, is to provide an improved expulsion type circuit interrupter which shall be capable of interrupting arcs of widely varying current magnitude-and which, at the same time, shall be provided with means for assuring that the normal efficiency of the device shall be unimpaired during its operation.

Another objectof my invention is to provide a device in which the arc is rotated during the arc extinguishing operation in order that it shall progressively contact fresh gas evolving material, thus assuring the generation of a sufllcient quantity of gas to effect a rapid extinguishment of the arc. The rotation of the are also increases effectiveness of the device due to the fact that the arc movement causes turbulence which aids in disrupting the ionized arc stream.

In carrying out these objects of my invention, I provide, in the preferred embodiment, a pair of tubular insulating members, one of which is larger than the other and is positioned concentric therewith. These tubular members define the surfaces of a pair of arc passages, one of which is substantially cylindrical in form and the other of which has the form of a hollow cylinder. The are drawing means is so arranged that a portion of the arc incident to the interruption of the controlled circuit is established within each. of the two are passages. The dimensions or the main passage are sufiiciently large that very rapid extinction of large magnitude arcs will be effected therein and the dimensions of the hollow cylindricalarc passage are such that arcs of small current magnitude as well as arcs of large current magnitude are caused to intimately contact the opposed surfaces which define that passage. Both of the arc passages are lined with a suitable gas evolving material for producing the desired expulsive gas blasts.

It will immediately be seen that this device combines the desirable features of the expulsiontype circuit interrupter which utilized a single cylindrical arc passage andthe newer form, mentioned above, which utilized a tubular arc passage, and it effects this combination without unreasonably increasing the cost of the device.

In order to prevent the erosion eifect, which, as mentioned above, is the principal undesirable feature of the tubular type device, I provide a suitable means for causing the arc to move laterally within the arc passage along the periphery of the surface defining means therefor, during .the operation of the device. This movement is best effected by a magnetic arrangement which provides a radial field in the region of the arc terminal within the arc passage, although other means could unquestionably be used. By causing small magnitude current arcs to move within the arc passage during the interruption thereof, local erosion is efiectively'prevented and the normal high efliciency of the device is maintained throughout its entire operative life.

Since, as pointed out above, one of the principal fields for immediate application of my invention is in connection with expulsion fuses, I shall hereinafter describe an embodiment of my invention as applied to such devices without, however, in any way intending to restrict the scope of my invention except as indicated n the appended claims.

Referring to the single sheet of drawings:

Figure 1 isan elevational view of an expulsion fuse wherein are embodied the principal elements of my invention;

Fig. 2 is a sectional view of the expulsion fuse shown in Fig. 1; I

Fig. 3 is a bottom plan view of the expulsion fuse shown in Figs. 1 and 2;

Fig. 415 a sectional view taken on theline IV-IV of Fig. 2; and

Fig. 5 is a detail view of the fusible element utilized for establishing the are within the device during the normal operation thereof.

The expulsion fuse shown in the drawing comprises generally a main tube l of fibre orlike insulating material which defines the outer walls of the main arc passage 2, the tube having suflicient strength to withstand the internal premures normally developed therewithin duringv the operation of thesedevices; a metallic cap or ferrule 3 for enclosing the upper end of the main insulating tube I an annular member 5015 conducting material, which is supported upon the main insulating tube by means such as the insulating screws 1, for providing the other terminal of the device; a second annular member 9 likewise supported upon the main insulating tube I by suit! able insulating screws ll and a second tube I3 also of fibre or like material for defining the outer walls of a second arc passage H. ,The upper end I5 of the main tube l is threaded and is adapted to engage suitable cooperating threads l1 formed in the upper ferrule 3. Similarly, the upper end I 9 of the other insulating tuoe I3 is threadedand engages cooperating threads 2| formediwithin the lower annular member 9.

A helical coil 23, one end of which is brazed or otherwise rigidly aflixed to the upper annular member 5 and theother end of which is similarly afllxed to the lower annular member 9, is provided for completing the electrical circuit between those members and for providing a radial field for moving the arc during the operation of the device. c

The fusible element 25 is shown particularly in Fig. 5. The upper end is adapted to be electrically 'connected to the top ferrule by suitable means such as the screw 21 and the lower end is adapted to engage a suitable recess 29 formed within the lower annular member 9. The'screw 3| is provided for securely holding the lower end of thefusible element within the recess 28. The fusible element 25 is provided with a pair of re stricted portions 33 and 35, the narrower of which (33) is adapted to be'disposed within the main fuse tube I and the least-restricted of which (35) is adapted to be disposed within the tubular arc passage I 4 adjacent the lower annular member 9.

The main tube I, as mentioned above, defines the walls of the main arc passage 2 whitzh is sub-; stantially cylindrical in form and in conjunc-r tion with the other tube l3 defines the second arc passage H which has the form of a hollow cylin-', der. It is preferable that these tubes be mounted substantially concentric with eachother in order that the width of the second arc passage l4 shall be uniform. Both of the tubes are preferably formed of fibre or a like material due to the fact that this material has a high mechanical strength and is inexpensive, and at the' same time, is capable of providing an adequate blast of arc extinguishing gas for extinguishing the arc. It is possible, of course, to make the outer tube l3 of a refractory material since the inner surface of the outer arc passage I 4 would be capable of evolving sufficient gas to effect the extinguishment of any arcs which might be established therein.

The electrical circuit through the fuse is com paratively direct. Beginning with the upper cap or ferrule 3 the current flows successively through the fuse element 25, the lower annular member 9 which serves as a support for the outer tube l3, the helical coil 23 intermediate the lower annular member 9 and the upper annular member 5 which serves as one terminal of the device, and thence through that member to the other side of the controlled circuit. The fuse may be supported upon suitable clips or the like, numerous satisfactory arrangements being well known in the art.

Upon the occurrence ofan overload in the circuit controlled by the device, the fusible element 25 melts and causes an arc to be established having a portion within each of the two are passages 2 and [4. If the magnitude of the current producing the melting of the fusible element 25 is large, both of the restricted portions 33 and 35 will fuse substantially at the same time, and the arc will be established simultaneously in both of the arc passages. Large magnitude arcs will substantially entirely fill the main cylindrical arc passage 2, and will also substantially fill the tubular arc passage M (the cross-sectional areas of those passages being substantially equal in the preferred form of-my invention), and by virtue of the intimate contact between the arc and the gas evolving lining of the two passages a large quantity of arc extinguishing gas will be evolved from the surfaces defining the walls of those passages. This gas will flow longitudinally through the two are passages, both of these passages being closed at the upper end, with an expulsive action and will thereby effect a rapid and positive extinguishment of the arc.

The reduced area portions 33 and 35 of the fusible element 25 are so correlated that the fusible portion 35 within the tubular arc passage M will melt somewhat later than the portion within the cylindrical arc passage 2, the difference in time being substantially inversely-pro-,

portional to the arc current. Thus, if the magnitude of the overload causing the fusing of the element 25 is comparatively small, the arc will be initially established within the cylindrical tube 2, and if it is not shortly thereafter extinguished, the reduced section 35 within the tubular arc passage M will melt, thereby establishing aportion of the are within that passage. The proximity of the walls of the tubular arc passage will assure an intimate contact between the arc and the gas evolving surfaces, which define that passage. Thus, even a small magnitude arc will cause the evolution of sufiicient quantities of arc extinguishing gas to effect a rapid and efllcient extinguishment of the are drawn therein. By delaying the establishing of low current magnitude arcs 'within tubular arc passage l4 until after the arc is established within the main arc passage, erosion of the walls of' within this are passage, the magnetic effect of the radial field produced by the helical coil 23 tions of low magnitude current arcs.

will cause the arc to move laterally within the tubular arc passage, the annular member 9 serving to provide a suitable terminal on which terminal the arc may move. This rotation of the arc prevents, as mentioned previously, any localized erosion of the walls which define the tubular arc passage and in combination with the delayed arc establishing action of the fusible element 25, assures that the normal eificiency of the device shall be maintained throughout its entire operating life.

During the extinction of both large and small magnitude current arcs, the unfused portions of the fusible element 25--if any such portions exist-are expulsively ejected from the arc passages 2 and H by virtue of the force exerted thereon by the outflowing blast of arc extinguishing gas.

From the foregoing, it will be seen that I have provided an improved expulsion type circuit interrupter which is capable of satisfactorily interrupting arcs of small and of large current magnitude and which does not have any of the disadvantages of the devices previously known to the art for accomplishing this. My improved circuit interrupter utilizes a pair of arc passages, one of which is substantially cylindrical in form and the other of which is substantially tubular in form, and a portion of the arc is drawn within each of the two passages. This arrangement assures an intimate contact between the arc and the surfaces of the arc passages regardless of the current magnitude of the arc. Further, by providing suitable means for rotating the portion of the are which is drawn within the tubular arc passage, I prevent localized erosion which might'cause the device to become inoperative after repeated interrup- Moreover, the structural features of my invention are comparatively simple, and the entire device is only slightly more expensive than the old form of a single arc passage arrangement. This assures a low initial cost and a low maintenance cost.

In the preferred embodiment of my invention, I have shown a device wherein the wall defining means for both of the arc passages is substantially cylindrical in form. It is, of course, within the province of my invention that other surface forms might be used, and it is my intention that the language of the accompanying claims (particularly the word tubular) shall include arrangements wherein the arc passages or the means defining those passages are not bounded by cylindrical surfaces.

While in accordance with the patent statutes, I have disclosed the foregoing details of a practical embodiment of my invention, it is to be understood that any of these details are merely illustrative, and that the broad features of my invention are capable of much wider adaptation than to the particular structure disclosed in this application. For example, it is entirely within the province of my invention that the features disclosed herein might be embodied within an expulsion type circuit interrupter utilizing liquid as the gas evolving means. I desire, therefore, that my invention shall be given the broadest reasonable construction, and that the claims shall be limited only by what is expressly stated therein and by the prior art.

I claim as my invention:

1. In an air breakcircuit interrupter; means, at least partially of insulating material for dewhich is open at one end to the atmosphere but is otherwise substantially completely enclosed; means, likewise at least partially of insulating material, positioned within said passageway, at least during the circuit interrupting operation, for defining the inner surface of said arc passage; means for establishing an are between said inner and said outer surfaces; and means for causing said arc'to be moved laterally in recurrent paths within said are passage; said surface defining means so restricting the volume of said passage that arcs of small current magnitude as well as arcs of large current magnitude are caused to intimately contact the surfaces defining said are passage during the circuit interrupting operation; at least a portion of one of said surface defining means being formed of a solid material which is capable of evolving an are extinguishing gas when placed in proximity to an electric arc.

2. In an air break circuit interrupter; means, at least partially of insulating material for defining the outer surface of a tubular arc passage which is open at one end to the atmosphere but is otherwise substantially completely enclosed; means, likewise a least partially of insulating material, positioned within said passageway, at least during the circuit interrupting operation, for defining the inner surface of said are passage;

- means for establishing an are between said inner and said outer surfaces; and magnetic means for causing said are to be moved laterally in recurrent paths within said tubular arc passage; at least a portion of one of said surface defining means being formed of a solid material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc.

3. In an air break circuit interrupter; means of insulating material for defining substantially closed outer side walls of an arc passage, 8. substantial portion of the inner surface of said wall defining means including a solid material that is capable of evolving an arc extinguishing gas when placed in proximity to an electric are; means for establishing an are within said are passage; means, a substantial portion of the outer surface of which is formed of an insulating material which is capable of evolving an are extinguishing gas when placed in proximity to an electric are, for so restricting the volume of said arc passage that arcs of small current'magnitude as well as arcs of large current magnitude are caused to intimately contact the gas evolving surfaces of said are passage during the circuit interrupting operation; and means for producing a radial magnetic field within said passage at least as soon as said are is established therein, said field causing said arc to move laterally along the periphery of said wall defining means in recurrent paths during the progress of each circuit interrupting operation. 7 1 4. In a circuit interrupter; means at least partially of insulating material for defining the outer .wall of an arc passage; hollow means likewise at least partially of insulating material, disposed within said wall defining means for defining the inner wall of said are passage and for defining the outer wall of a second arc passage; and means for establishing an are having a portion in each of said passages during the operation of said interrupter; said second arc passage being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude; the physical dimensions of fining the outer surface of a tubular arc passage said first arc passage being so restricted by the arc passage and thereby be extinguished; said first arc passage, at the same time, having sufiicient volume to accommodate such arcs of large current magnitude as may be established therein during the operation of said interrupter.

5. In a circuit interrupter, tubular means of insulating material for defining the outer wall of an arc passage; a second tubular means disposed within said first tubular means for defining the inner wall of said are passage and for defining the outer wall of a second arc passage; and means for establishing an are having a portion in each of said arc passages during the operation of said interrupter; a substantial portion of the surfaces defining said are passages including a solid material that is capable'of evolving considerable quantities of an arc extinguishing gas when placed in proximity to an electric are.

6. In a circuit interrupter, tubular means of insulating material having a substantially cylindrical opening therein for defining the outer wall of an arc passage; a second tubular means, also substantially cylindrical in form, disposed within and substantially concentric with said cylindrical opening for defining the inner wall of said arc passage and for defining the outer wall of a second arc passage; means for establishing an are having a portion in each of said are passages during the operation of said interrupter; and means for laterally moving that portion of said are which is established within said first arc passage during the circuit interrupting operation; a substantial portion of the surfaces defining said arc passages including a solid material that is capable of evolving considerable quantities of an arc extinguishing gas when placed in proximity to an electric arc.

v 7. In an expulsion type circuit interrupter; tubular means of insulating material for defining the outer wall of an arc passage; a second tubular means disposed within said first tubular means for defining the inner wall of said are passage and for defining the outer wall of a secleast during each operation of said interrupter,

and each of said arc passages being otherwise substantially completely enclosed; a substantial portion of the surfaces defining said are passages being formed of a solid material that is capablepf evolving considerable quantities of an arc extinguishing gas when placed in proximity to an electric arc; said second tubular.

means so restricting the volume of said first arc passage that arcs of small current magnitude are caused to intimately contact the surfaces defining said passage; said first passage, however;

" the inner surface of the smaller tube and the other of which is defined by the space between said concentric tubes; means for closing one end of both are passages, the other end being open during the circuit interrupting operation; and 15 two arc passages one of which is definedby the inner surface of the smaller tube and. the other of which is defined by the space between said concentric tubes; means for closing one end of both arc passages, the other end being open during the current interrupting operation; and

means for establishing an are having a portion in each of said are passages; a substantial por tion of the surfaces which define said are passages being formed of a solid material which evolves considerable quantities of an arc extinguishing gas when placed in proximity to an electric are. I

10. In an expulsion type circuit interrupter; a pair of concentric tubes for defining the walls of two are passages, one of which is defined by the inner surface of the smaller tube and the other of which is defined by the space between said concentric tubes; means for closing one end of both are passages, the other end being open during the circuit interrupting operation; means for establishing an are having a portion within each of said arc passages; and means for causing the portion of said arc which is established within said second arc passage to be laterally moved between the opposed concentric surfaces which define that passage during the circuit interrupting operation.

11. In an expulsion type circuit interrupter; a pair of concentric tubes for defining the walls of two arc passages, one of which is defined by the inner surface of the smaller tube and the other of which is defined by the space between said concentric tubes; means for closing one end of both arc passages, the other end being open during the circuit interrupting operation; means for establishing an arc having a portion within each of said are passages; and magnetic means for causing the portion of said arc which is established within said second arc passage to be laterally moved between the opposed concentric surfaces which define that passage during the circuit interrupting operation; a substantial portion of the surfaces which define said are passages being formed of a solid material which evolves considerable quantities of an arc extinguishing gas when placed in proximity to an electric arc.

12. In an expulsion type circuit interrupter; tubular means of insulating material for defining the outer wall of an arc passage; a second tubular means, of substantially greater length than said first-mentioned tubular means, disposed within said first-mentioned tubular means for defining the inner wall of said first-mentioned arc passage and the outer wall of a second arc passage; means for establishing an are having a portion in each of said arc passages during the operation of said interrupter; a cap member positioned at one end of said second tubular means for closing that end thereof and for providing a terminal for said interrupter; said second arc passage being open at the other end thereof, at least during each operation of said interrupter, and being otherwise substantially completely enclosed; a ferrule disposed on said second tubular member intermediate the ends thereof for providing the other terminal for said interrupter; an annular cap member, which serves to close one end of said first-mentioned arc passage, supported on said second tubular member a short distance from said ferrule; said first-mentioned arc passage being open at the other end thereof, at least during each operation of said interrupter, and being otherwise substantially completely enclosed; and a coil means positioned about said second tubular means intermediate said ferrule and said hollow cap, said coil means being permanently connected in series with, the electrical circuit through said interrupter and serving to provide a radial magnetic field within said firstmentioned are passage for laterally moving the portion of the are which is drawn therein.

13. In an expulsion type circuit interrupter;

cylindrical means of insulating material for dethan said first-mentioned cylindrical means and of less diameter than that means, disposed with in and concentric with said first-mentioned tubular means for defining the inner wall of said firstmentioned are passage and the outer wall of a second arc passage; means for establishing an are having a portion in each of-said arc passages during the operation of said interrupter; a cap member positioned at one end of said second cylindrical means for closing that end thereof and for providing a terminal for said interrupter; said second arc passage being open at the other end thereof, at least during said operation of said interrupter, and being otherwise substantially completely enclosed; a ferrule disposed on said second cylindrical member intermediate the ends thereof for providing the other terminal for said interrupter; an annular cap member, which serves to close one end of said first-mentioned arc passage, supported on said second cylindrical member a short distance from said ferrule;

said first-mentioned arc passages being open at the other end thereof, at least during each operation of said interrupter, and being otherwise substantially completely enclosed; a substantial portion of the surfaces which define both of said are passages being formed of a solid material which evolves considerable quantities of an arc extinguishing gas when placed in proximity to an electric arc; and coil means having the substantial form of a helix positioned about said tially closed except at one end, means including a fusible element for establishing an arc within said tubular passage and means for producing a magnetic field radially across said passage for moving said are laterally along the passage.

15. In a circuit interrupter, means of insulating material for defining an endless arc passage of tubular form, said passage being substantially closed at its sides and at one end, means gincluding a fusible element for-establishing an arc within said tubular passage and means for producing a magnetic field radially along the passage, said tubular passage being restricted in width to such an extent that arcs of variable current magnitude are caused to intimately engage the opposed walls thereof and means in 'cluded within the walls of said passage which produces a gas when acted upon by said arc to aid in extinguishing the are.

16. In a circuit interrupter, means 01 insulating material for defining the walls of a cylindrical are passage and a tubular recurrent arc passage surrounding the cylindrical passage, a fusible element lying partially in said cylindrical arc passage and partially in said tubular arc passage for establishing an are within said respective passages, means for producing a mag- 'member surrounding inpart said first tubular member, 'a second terminal member for enclosing one ,end of the passage between said tubular members and for supporting .said second terminal member in spaced relation with respect to said first tubular member, a fusible element lying partially in one tubular member and partially in the other and secured at its ends to said terminal members, said fusible element being adapted to establish an are within both of said tubular members and a coil surrounding said first tubular member connected in series with said second terminal member for producing a radial magnetic field within said second tubular member to cause the arc to be rotated therein.

18. In a circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing two coaxial bores, and means for initiating an arc first in one bore and then in the other bore.

19. The combination of claim 18, wherein the two arcs are formed at the same end of both bores. I

20. In a, circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing two coaxial bores one of which provides a passage of greater width for the arc than the other, and means for initiating an arc first in the bore providing the passage of greater width and then in the other bore.

21. In a circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing twocoaxial bores each of which is open at one end and substantially closed at the other end at least during the arc extinguishing period, and means for initiating an arc first in one bore and then in the other bore. v

22. In a circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing two coaxial bores one of which provides a passage of greater width for the arc than the other, and each of which is open at one end and substantially closed at the other end at least during the arc, extinguishing period, and means for initiating the arc first in the bore providing the passage of greater width and then in the other bore.

23. In a circuit interrupter, relatively separable terminals, are extinguishing means associated with said terminals providing two coaxial bores one or which provides a passage or greater width for the arc than'the other, each of said bores having a solid material therealong which gives ofl gas when acted upon by an arc, and means for initiating an arc first in the bore 'providing the passage of greater width and then in the other bore.

24. In a circuit interrupter, means of insulating material for defining the wall of a first arc passage, means of insulating material within said first arc passage for defining the wall of a second are passage, means for establishing an arc in each of said are passages, one of said arc passages being so narrow'that arcs of small current magnitude are readily extinguished therein and the other of said are passages being so wide as to accommodate arcs of large current magnitude, and said means for establishing the are causing the arc to be first established in the wide arc passage.

25. In an expulsion circuit interrupter, means of insulating material for defining the wall or a first arc passage, means of insulating material within said first arc passage for defining a second arc passage, means for establishing an arc in each of said are passages, each of said are passages having included in its wall a material formed. u

26. In an expulsion circuit interrupter, means of insulating material for defining the wall of a first arc passage, means of insulating material within said first arc passage for defining a second arc passage, means for establishing an arc in each of said arc passages, each of said are passages having included in its wall a material which gives. off gas when acted 'upon by an arc and being open at one end at least when the arc is being extinguished therein to permit a blast of gas to fiow through the arc, and one of said arc passages being so narrow that arcs of small current magnitude intimately contact its wall and the other of said passages being of sufllcient width to accommodate arcs of high current ma nitude without destructive pressures being formed, and said'means for establishing the are causing the arc to be first established in the passage for pair of tubular members one within the otherin spaced relation providing a pair of arcing chambers having inner surfaces iormed by solid arc extinguishing material from which an arc extinguishin'g medium is 'evolved by the heat of an are formed therein, means closing one end of each tubular member while the other end of each is open, and means in each chamber adapted to form an are under predetermined operating conditions, relatively small current arcs being more readily extinguished in one arcing chamber and relatively large current arcs being more readily extinguished in the other arcing chamber.

28. In a circuit interrupter, in combination, a

spaced relation providing a pair or arcing chambers having inner surfaces formed by solid arc ends of said tubular members while the other 76 ends remain open, and fusible means 01' different current carrying capacity in each arcing chamber, the opposite walls of one arcing chamber being relatively close together for extinguishing relatively small current arcs and the Opposite walls of the other arcing member being relatively far apart for extinguishing relatively large current arcs.

29. In a circuit interrupter, in combination,

are extinguishing means providing two coaxial bores open at one end and closed. at the other, and means adapted to form an arc in each bore on operation of the interrupter, relatively small current arcs being extinguished in one bore and 6 relatively large current arcs being extinguished in the other bore.

LEWIS R. SMITH. 

